<VV> Corvair compression readings

[keith osborne]

But remember also that a camshaft with a profile such that it improves performance accomplishes this not only through higher valve lift, but also by opening the valves sooner, and more importantly for this discussion, closing them later.  

Again, for the purpose of this discussion, at higher engine speeds, the inertia of the intake stream keeps air flowing into the cylinder well after the piston is on it's way up, on the compression stroke.  At cranking speed, this does not happen.  

So when comparing a stock cam to a performance cam- all other things being equal- compression readings will be lower for the performance cam.

I can vouch specifically for the reduced compression braking effect, though personal experience-  Many years ago, I built a dune buggy with a 145 ci early engine.  The engine was really tired, so I pulled it apart, and put rings and bearings in it.  While I had it apart, I also put a 140hp cam in it, just because I had one.  That engine ran very well, and delivered very good compression braking, while descending steep dunes.

Later I put together a 164 ci late engine, with 140hp heads, with new pistons (I think it was actually 166 ci at that point), rings and bearings, and an OT 30 camshaft.  That engine ran really, REALLY well, and provided dramatically less braking while descending those same steep dunes, in the same car.

Keith